In which form do the majority of carbon dioxide molecules exist in the body?

The majority of carbon dioxide molecules in the body exist in the form of bicarbonate ions. When carbon dioxide is produced by cellular metabolism, it diffuses into the bloodstream. A significant portion of this carbon dioxide reacts with water to form carbonic acid through the action of the enzyme carbonic anhydrase. Carbonic acid is then in equilibrium with bicarbonate and protons. The reaction primarily takes place in red blood cells, where carbon dioxide is converted to bicarbonate ions and transported in the plasma.

The bicarbonate ion is the predominant form of carbon dioxide in the body, accounting for about 70% of the total carbon dioxide transported in the blood. This conversion plays a critical role in maintaining acid-base balance (pH) in the body, as bicarbonate acts as a buffer.

Other forms of carbon dioxide, such as dissolved gas and carbonic acid, exist in smaller amounts. Dissolved carbon dioxide, which accounts for a minor percentage, is simply carbon dioxide that remains in the gas form and is less relevant to transport mechanisms compared to bicarbonate. In this context, understanding the predominant role of bicarbonate ions is crucial for grasping the physiological aspects of carbon dioxide transport and acid-base regulation in the body.